[IShouldBeRevising_]

BF3 has 3 bonded pairs and 0 lone pairs

NH3 has 3 bonded pairs and 1 lone pair

BF3 bond angle = 120

Each lone pair reduces bond angle by 2.5

So why isn't NH3 bond angle 117.5 but instead it is 107?

[Smiley Face :)]

NH3 has 3 bonding pairs of electrons and 1 lone pair.
Therefore its based on a tetrahedral shape... which have bond angles of 109.5
But due to the repulsion of the lone pairs you have to minus 2.5 as they have greater repulsion than bonded electrons
So u get a bond angle of 107 degrees

[IShouldBeRevising_]

(Original post by Smiley Face :))
NH3 has 3 bonding pairs of electrons and 1 lone pair.
Therefore its based on a tetrahedral shape... which have bond angles of 109.5
But due to the repulsion of the lone pairs you have to minus 2.5 as they have greater repulsion than bonded electrons
So u get a bond angle of 107 degrees

Ohhhhhh thanks!

[UnknownGirly]

CH4 has a bond angle of 109.5 degrees. Take away one a hydrogen, and you get a lone pair. Reducing the bond angle by 2.5 degrees - making it 107 degrees.